Update hooks.rst (#6160 / #6161)

This proposed update is in regard to Issue #6160

CONTRIBUTORS.rst

@@ -467,6 +467,7 @@ Contributors
 * Yngve Høiseth
 * Andrew Bunker
 * Nikolay Lukyanov (mozgsml)
+* Jean Zombie
 
 Translators
 ===========

docs/reference/hooks.rst

@@ -27,7 +27,7 @@ Alternatively, ``hooks.register`` can be called as an ordinary function, passing
 
   hooks.register('name_of_hook', my_hook_function)
 
-If you need your hooks to run in a particular order, you can pass the ``order`` parameter:
+If you need your hooks to run in a particular order, you can pass the ``order`` parameter.  If order is not specified then the hooks proceed in the order given by INSTALLED_APPS. Wagtail uses hooks internally, too, so you need to be aware of order when overriding built-in Wagtail functionality (i.e. removing default summary items):
 
 .. code-block:: python